1. Field of the Invention
The present invention relates to a technique for creating a virtual object in a composite space of a physical space and a virtual space.
2. Description of the Related Art
In the manufacturing design field, a three-dimensional CAD system has conventionally been used to design a three-dimensional model. In the conventional three-dimensional CAD system, when the operator creates a three-dimensional model using a display (monitor) and a mouse, he or she generally sets a plane to serve as a reference, creates the bottom surface of a three-dimensional model on the plane, and determines its height, thereby generating a three-dimensional model.
Also, a system capable of using an HMD (Head-Mounted Display) to design a three-dimensional model using a three-dimensional CAD system in a virtual reality space is under study (non-patent literature 1 (Tomoyuki Inoue, Naoki Nishizumi, Nobuaki Suzuki, Naofumi Yasufuku, and Sato Saga, “Proposal of 3-D Modeling Interface ‘BlueGrotto’ on the Basis of Drawing Gesture Identification in Virtual Space”, IEICE Trans. (D-II), J87-D-II, 6, (2004-06), pp. 1,309-1318)).
Moreover, a system capable of creating a model as long as the operator simply draws the contour of a three-dimensional model that he or she wants to generate is under study (non-patent literature 2 (T. Igarashi, S. Matsuoka, and H. Tanaka, Teddy: A sketching interface for 3D freeform design. In SIGGRAPH '99 Proceedings, pp. 409-416, 1999)) in order to easily create a three-dimensional model without requiring expertise on the side of the operator in a design system such as three-dimensional CAD.
On the other hand, in recent years, studies pertaining to an MR (Mixed Reality) are being actively conducted, with the aim of seamlessly combining a physical space and a virtual space. An image display apparatus which presents a mixed reality has, for example, the following configuration. That is, this device displays an image in which a virtual space image (for example, a virtual object or text information rendered by computer graphics) generated in accordance with the position and orientation of an image sensing device such as a video camera is superimposed and rendered on a physical space image sensed by the image sensing device. An HMD (Head-Mounted Display), for example, can be used as this device.
This image display device can also be implemented by a scheme in which a virtual space image generated in accordance with the position and orientation of the viewpoint of the operator is displayed on an optical see-through display mounted on the operator's head.
Various interfaces used to manipulate a virtual reality space or a mixed reality space have been proposed for an image display device which presents the virtual reality space or the mixed reality space to the operator (patent literature 1 (Japanese Patent No. 03944019)). With a combination of the above-mentioned techniques, a three-dimensional model can be created in a virtual reality space or a mixed reality space.
In a conventional method, when the operator creates a virtual object in a virtual reality space or a mixed reality space, he or she performs modeling using an arbitrary plane determined in advance as a reference. With this method, it is possible to create a virtual object on an arbitrary plane, but it is difficult for the operator to create a virtual object at a position where he or she wants to create it in a virtual reality space or a mixed reality space. At this time, when the operator creates a virtual object, it is necessary to automatically determine an arbitrary plane by an operator's operation to allow creation of a virtual object.